1. Field of the Invention
The present invention relates to a battery. More particularly, the present invention relates to a battery configured to have an increased power capacity, the battery having a battery case housing an electrode assembly and an electrolyte, and a cap assembly including a cap plate for covering the battery case.
2. Description of the Related Art
Batteries are employed in a wide variety of equipment including, to name just a few, vehicles, e.g., electric and hybrid vehicles, portable power tools, electronics, etc. Portable compact electronic devices, e.g., cellular phones, laptop computers, camcorders, etc., are being widely developed and produced. Such portable electronic devices typically include an internal battery pack to allow continuing operation even when no external power supply is available. Such a built-in battery pack typically includes at least one unit battery inside and provides the electronic device with a predetermined level of voltage over a reasonable period of time.
Batteries are generally classified as primary or secondary batteries. Primary batteries are commonly known as single-use batteries, while secondary batteries are commonly known as rechargeable batteries. Both primary and secondary batteries may be suitable for use in portable electronic devices. However, secondary batteries are widely adopted because they can be reused and may be, therefore, more economical than single-use batteries. Secondary batteries have been developed using a wide variety of technologies.
Battery technologies currently favored for portable electronic devices include nickel cadmium (Ni—Cd) batteries, nickel metal hydride (Ni-MH) batteries, lithium (Li) batteries, etc. The Li batteries have, in particular, been widely employed in the latest generation of electronics devices. A Li battery may have an operation voltage of 3.6V, which is about three times the operation voltage of comparable Ni—Cd or Ni-MH batteries. The Li battery may exhibit a relatively high energy density per unit weight. In a typical Li battery, a lithium-based oxide may be used as a positive electrode activation material, and a carbon-based material may be used as a negative electrode activation material. Li batteries may be classified as liquid electrolyte batteries and polymer electrolyte batteries, depending on the electrolyte used therein. Liquid electrolyte batteries are also known as lithium ion (Li-ion) batteries and polymer electrolyte batteries are also known as Li polymer batteries. The Li battery may be manufactured in various shapes, e.g., cylindrical can types, rectangular or prismatic can types, pouch types, etc.
A typical battery may have an electrode assembly, a battery case for housing the electrode assembly and electrolyte injected inside the battery case to give mobility to charge carriers, e.g., ions. The electrode assembly may include a positive electrode plate on which a positive activation material is coated, a negative electrode plate on which a negative activation material is coated and a separator interposed between the positive and negative electrode plates. The separator may serve to prevent short circuits between the positive and negative electrode plates, and to allow only charge carriers to pass. The width of the separator of the electrode assembly may be larger than the widths of the electrode plates, in order to prevent the electrode plates from making contact with each other.
The electrode assembly of the battery may be fabricated by stacking the positive and negative electrode plates with the separator interposed therebetween, and the resulting structure may be wound into a jelly roll configuration. Positive and negative electrode taps may extend from the positive and negative electrode plates, respectively, in order to allow electrical connections to the electrode plates.
One of the positive and negative electrode taps may be connected to the cap plate of the cap assembly. The cap plate may be electrically connected to the battery case, so that the battery case may act as an electrode terminal. The other of the positive and negative taps, i.e., a tap of the opposite polarity, may be connected to another electrode terminal, which may be insulated from and pass through the cap assembly.
The cap assembly may include the cap plate, which may be assembled to the battery case to cover it. The cap plate may be welded to the battery case. The cap plate may cover an opening in the battery case through which the electrode assembly is installed.
The cap assembly may further include an electrode terminal passing therethrough, and a gasket installed between the cap plate and the electrode terminal for electrically insulating them from each other. The cap assembly may also include an insulation plate providing insulation between the cap plate and the electrode tap of opposite polarity, and a terminal plate installed in a lower portion of the insulation plate and connected to the electrode terminal.
The electrolyte may be injected into the battery case after the electrode assembly is placed in the battery case. The electrolyte allows charge carriers, e.g., ions, to travel between the positive and negative electrode plates. The electrolyte may occupy all of the remaining volume within the battery case.
Battery capacity is determined by a number of design factors including, e.g., the battery technology (chemistry) employed, the sizes of the positive and negative electrode plates, the electrolyte, etc. For a given battery technology, battery capacity is generally limited by the size of the battery. Accordingly, where the size of the battery is limited by, e.g., the design limitations of the device it is intended to power, it may be difficult to increase the battery capacity.
For example, if the amount of the electrolyte in the battery is insufficient, the capacity of the battery may be reduced. Further, in the case of a secondary battery, which may be discharged and charged numerous times, the capacity of the secondary battery may be reduced over time if the electrolyte begins to deteriorate with use. Increasing the size of the battery case to provide a sufficient amount of electrolyte may not be possible if the design requirements of the electronic equipment do not allow for a larger battery. Moreover, reducing the size, i.e., volume, of the charge-generating positive and negative electrode plates may allow for more electrolyte, but may reduce the overall capacity of the battery. Therefore, there is a need for a battery that maximizes the available electrolyte volume without increasing the external dimensions of the battery or reducing the size of the charge-generating elements therein.
One possible approach to increasing the internal volume of the battery is to reduce the thickness of the cap plate, i.e., thin the inner surface of the cap plate. However, if the cap plate is welded to the battery case, reducing the thickness of the cap plate may make it difficult to weld the cap plate to the battery case. In particular, the cap plate may be damaged by the welding process, even if a low power welding apparatus is employed, leaks may develop at the welded seams due to the thinning of the cap plate, etc.